A pressure sensor includes a metal stem having a diaphragm for a pressure detection, a semiconductor substrate attached to a surface of the diaphragm, and strain gauges for converting a bending of the diaphragm formed on the semiconductor substrate to an electrical signal (for example, JP-B2-7-11461 which corresponds to U.S. Pat. Nos. 4,986,861 and 4,840,067).
In the pressure sensor, the thickness of a bending portion is constructed with the thickness of the diaphragm and the thickness of the semiconductor substrate. In this case, it is necessary for both the diaphragm and the semiconductor substrate to make thinner in order to increase a sensor sensitivity. However, when the semiconductor substrate is made thinner, the strength of the semiconductor substrate is greatly deteriorated.
Furthermore, when the strain gauges are constructed with a diffused resistor that is formed using a semiconductor process, electrical insulation of the strain gauges is generally performed by PN junction. In this case, a leak current may be generated on the PN junction portion at a high temperature, and it is difficult to accurately detect the pressure at a high temperature environment.